Salinity is one of the most severe factors that limits the yield of filed, because most of crops employed in agriculture is salt sensitive. This losses in yield is mainly due to drought and high salinity of field and this situation will be worst with global climatic changes. In particular the toxicity of Na⁺ is due to its ability to inhibit enzyme function directly by binding to inhibitory sites or indirectly by displacing K⁺ from activation sites. Plants have evolved a wide range of mechanisms to adapt and mitigate this kind of abiotic stress. Here we reviewed sensing and signaling mechanisms of salt stress and the tolerance strategies in plants.

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In this concept paper, a review on the history of mathematical handling of photosynthesis using kinetic equations and the repetition of classical experiments for renewing the discussion on the plant canopy photosynthesis are combined. In the upper half of this article, we reviewed the century-old history of the use of equations in photosynthetic analyses inspired by the mathematical models by A. V. Hill. Then we tried to challenge the 80-year-old mystery of Boysen-Jensen's plant canopy photosynthesis proposed by Boysen-Jensen in 1932, which induced a series of discussion if the nature of photosynthetic irradiation (PI) response in the plant canopy is largely differed from the one in a single leaf. Despite long-lasted belief, we concluded that there would be no mystery in the canopy photosynthesis. We assumed that the apparent lack of saturation in PI-curves in a stand of plant could be attributed to, neither the temporal movements of leaves nor the alteration of the sun's position, despite the earlier suggestion by Monsi and Saeki who assumed utilization of scattered sun light by plants, but it could be simply an artifact due to the lack of consideration on the positional effect of broad beam-angled artificial light source. Lastly, we revised the photosynthetic modes under layers of leaf canopies by proposing a set of practitioner-friendly mathematical model which could be applicable for estimating the total photosynthesis in the plant canopy structure consisted with layer of inclined leaves. Newly proposed equations can be used for simulation of the photosynthetic capacity in the plant canopy structure simply through measurements of (1) the PI-curve, (2) the state of respiration, and (3) transmittance in a single top-positioned leaf consisting the canopy structure.

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Polyamines (PAs) are small, aliphatic amines that are found in all living cells. In plants, putrescine, spermidine, spermine, and thermospermine are known as ubiquitous PAs. They are involved in various physiological processes and environmental stress responses, including pathogen infections. Several studies have demonstrated that PAs and their catabolic products, such as H ₂O ₂ produced by diamine oxidases and polyamine oxidases, are closely involved in the activation of host defense mechanisms. This minireview briefly summarizes recent advances regarding the function of PAs during disease resistance in plants.

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Salinization is one of the main environmental constraints that threat global crop biomass production. Halophytic species are currently widely studied because of their value for the development of saline agriculture. In this study we investigated the impact of repetitive salt shocks to mimic inundation with seawater and recorded changes in ionic and water status, growth parameters and some markers of oxidative stress of sea rocket, Cakile maritima, succulent halophyte which displays potential for economical nutrient food, for therapeutic utilization and for it seeds contain up to 40% of oil. Cakile maritima displayed different growth behavior in response to salt shock. Repetitive salt shocks with NaCl concentrations superior to 200 mM induced a reduction of growth of aerial parts. For the lower concentrations of NaCl (50–100 mM), we observed slight but not significant growth stimulation. Under salt shock, C. martima maintained hydration in the aerial parts despite their high contents in sodium and chlorine. Changes of malondialdehyde (MDA) and ascorbic acid under salt shock revealed beneficial and damaging functions of these molecules at low and high salt shock, respectively.

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The marine diatom Phaeodactylum tricornutum is expected to be a source of hydrocarbons and carotenoids that are synthesized via isoprenoid precursor biosynthesis pathways such as the mevalonate (MVA) and the 2-C-methyl-D-erythritol phosphate (MEP) pathways, because the molecular biotechnological techniques for metabolic engineering have been established. In this study, we investigated the expression profiles of the genes, including those in the MVA and MEP pathways, under various culture conditions using RNA-seq analysis to obtain information useful for the metabolic engineering and development of endogenous promoters that can highly drive the expression of transgenes in P. tricornutum. The expression levels of the genes in the MVA pathway, except for the 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR) gene, were low under all the conditions tested, and the expression levels of the 4-diphosphocytidyl-2-C-methyl-D-erythritol kinase (CMK) and 2-C-methyl-D-erythritol 2,4-cyclodiphosphate synthase (MDS) genes in the MEP pathway were relatively low. Eleven genes with high expression levels, including the V-type proton ATPase subunit C-like gene, which are potential sources of endogenous promoters in P. tricornutum, were selected. These results are expected to provide useful information for the metabolic engineering of P. tricornutum.

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X-ray high resolution three-dimensional computed tomography (XHR3DCT) is a non-invasive technique to monitor the inner morphology of an object. It permits to obtain a series of horizontal stack of the structure that allows its 3D reconstruction of images by a computer post-processing analysis. This technology is commonly used for medical analysis on human or rarely on animals and its utilization in the plant field has been recently discussed. As we are engaged in the investigation on the possibility to use XHR3DCT for monitoring the storage quality and/or post-harvest development of fresh produces such as vegetables, here we report on minimal demonstration performed on garlic bulbs. In particular, immediately after the harvest from the soil, cloves of garlic bulbs have been maintained under different conditions differed in temperature and humidity, with and without irradiation by red (660 nm) or infra-red (735 nm) lights. At an intermediate time, some cloves have been non-invasively monitored by XHR3DCT to predict the changes in the size (volume) of growing inner shoots (sprouts). To determine the sprout volume based on the XHR3DCT-scanned images, several mathematical approaches have been tested. With approximation of the garlic sprout shape as a parabolic cone, estimation of shoot volume could be readily achieved. By analyzing the inner shoot size in garlic clove kept under different conditions, increase in the shoot size under red light or under higher temperature and relative humidity could be monitored non-invasively, suggesting that XHR3DCT can be used for monitoring of inner structure within the clove of garlic without damaging the samples. Future applications of this technique in during post-harvest managements of a wide range of fresh produces are expected.

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Some of the plant species including embryophytes (especially, bryophytes and ferns) utilize the sperms but not pollens for their sexual reproduction. Because sperm motility is one of the most important features for the fertility in human and animals, percentage of motility and the kinetic parameters for swimming and the guidance to eggs (taxis) are well focused in the field of reproductive biology to evaluate and improve the male infertility. However, the nature of plant sperms is rarely known even more than a century has passed since the first microscopic observations of sperms in embryophytes as in the cases in Ginkgo biloba and Cycas revoluta, commonly known as sperm-generating plant species, have been made in the end of 19th century. In the present study, we performed high throughput analysis on the sperm motility in the most common liverwort, Marchantia polymorpha L. using a Computer-Assisted Sperm Analyzing (CASA) system. Time-dependent changes in kinetic parameters of Marchantia sperm motility from high to low motility states suggested that amplitude of lateral head displacement, rather than its frequency play key roles in the speed and distance of swimming at high motility state. From the average lifetime of high motility state and the speed of migration, the distance traveled by Marchantia sperms, due to their own motility, are estimated to be less than 3 cm, suggesting that motility of Marchantia sperms might mainly play a key role in the final fertilization step, but not in the long-distance travelling from the patchily distributed colonies of male strains to those of female strains, often being apart by few meters in the field.

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In many root tropic behaviors, auxin is the essential phytohormone to regulate a cell growth directing root development. It was reported that light promotes the translocation of auxin carrier proteins such as PINs (PIN-FORMED) providing a polarity for roots to complete negative phototropism. These PIN proteins are known to be translocated via endocytic vesicle recycling in root cells. However, an direct influence of light conditions on endocytic vesicle recycling mechanism controlling tropic behaviors in Arabidopsis root cells are not well assessed. In this study, we compared the activity of endocytic vesicle recycling and PIN2 localization in root cells at root transition zone grown under (1) light regime (16 h light / 8 h dark) for 5 d, (2) light regime for initial 4 d followed by 24-h of dark, and (3) continuous dark for 5 d. In the result, dark-grown seedlings showed lower rate of endocytotic activities in root transition zones, compared to the light-grown roots. Interestingly, light-promoted endocytic recycling activity was attenuated to the level equivalent to dark-grown roots after 24-h of dark treatment. PIN2-GFP was shown to accumulate in vacuoles both in dark-grown and 24-h dark treatment seedlings. Moreover, the PIN2-GFP signal found in 24-h dark-treated roots was stronger than in the dark-grown sample. Here we propose a model for dynamic regulation of PIN2 localization regulated by endocytic vesicle recycling in the transition of light circumstances, which might be important for roots to prepare for upcoming unfavorable light.

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Ferulic acid (FA) is one of phenolics found in most higher plants. It is important to quantify the internal FA level in vegetables and fruits, since it was epidemiologically demonstrated and a number of study supported that consumption of fruits and vegetables rich in phenolic acids including FA is associated with the prevention of chronic diseases such as cancer and cardiovascular disease. In order to allow handling of the intact fresh produces, non-invasive methods are desired. Previously, 355 nm ultraviolet (UV) laser-induced fluorescence spectrum revealed that living plants contain fluorophore corresponding to blue-green fluorescence (shown to be FA). However, quantification of FA based on fluorescence in UV-excited leaves can be hardly achieved since FA fluorescence measured at fixed excitation and emission can be applied only to the limited range of FA concentration. Here, we report a model experiment for fluorometric quantification of FA in solution in vitro which may provide a series of useful information required for estimation of FA concentrations in vivo fluid inside the vegetables. Based on deconvolution of intrinsic fluorescence spectra, we observed that FA fluorescence signals can be deciphered to determine the concentration of FA. By viewing that the recorded FA fluorescence (h) is reflecting the primitive function (f) corresponding to FA concentrations and kernel function (g) determining the spike position in the spectra. Thus, f should be obtained as f=h×g⁻¹. In practice, cumulative curves of fluorescence signals at fixed emission wavelength (460 nm) along with the changes in excitation wavelength (200–400 nm) were plotted and the midpoints (along the scale of excitation wavelength) in the resultant curves corresponding to different FA concentration were graphically determined. FA’s concentration-specific changes in fluorescence profiles must be due to the fact that FA possesses multiple fluorophores within the molecule despite its simple structure. Lastly, simplified protocol for determination of FA concentration using dual UV excitation wavelengths was proposed. In this assay, ratio of 460 nm fluorescence intensities induced by two distinct excitation wavelengths (short, 260 nm; long, 330–380 nm) were shown to be highly correlated with FA concentration ranged from μM to mM orders.

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Sixteen plant species were tested for their potential to remove radioactive cesium from contaminated soil with the Fukushima Daiichi nuclear disaster. There was a large difference of transfer factor (TF) of radiocesium (¹³⁷Cs) from the soil to plants. Among the examined plants, Hollyhock belonging to Malvaceae showed the highest TF but the efficiency of phytoremediation, such as total ¹³⁷Cs absorption of a plant or ¹³⁷Cs removal from unit area, was not proportionally high. According to the evaluation criteria (uptake of ¹³⁷Cs per plant and/or area), Kochia was shown to be the best plant species among 16 plants investigated here. Analysis of correlation showed that there was positive relationship between the total ¹³⁷Cs absorption and plant biomass, and contribution rate of plant biomass in total ¹³⁷Cs uptake by plant was scored to be 91.3%. These results indicate that selection of plant species that shows high biomass on site is important for ¹³⁷Cs-targeted phytoremediation rather than the plants’ ability in ¹³⁷Cs-uptake. On the other hand, our results also suggested that the TF value should be considered in order to evaluate the plant ability for ¹³⁷Cs-targeted phytoremediation. From this point of view, the present study suggests that field-grown Kochia could be used as a potential candidate plant for phytoremediation of ¹³⁷Cs from soil.

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For the decomposition organic substrates in the reaction container, we developed Ce-doped titanate nanotubes as visible light responsive photo catalyst. Anatase titania and titanate nanotubes were prepared using the sol-gel method and hydrothermal method. The photoactivity of Ce-doped titanate nanotubes under visible light were dramatically improved than anatase titania and titanate nanotubes. All titania and titanate nanotubes were characterized using X-ray diffraction, field emission scanning electron microscopy, inductively coupled plasma-atomic emission spectroscopy and UV-Vis absorption spectroscopy. Their's photocatalytic activities were investigated by the degradation rate of methylene blue solution under UV and visible light condition. The crystalinity of the titanate nanotubes were increased by Ce-doping compared with that of pure titania nanotube. In addition, the UV-Vis absorption ranges of Ce-doped anatase titania and Ce-doped titania nanotube were red shifted by Ce-doping. These morphology changes to nanotubes with Ce-doping will be very useful for practical application for decomposing color dyes included amino group in the wasted water.

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Recently, large-scale forest fires have been occurring frequently worldwide. In forest fires, the use of the firefighting foam has greatly improved fire extinguishing effects, but the environmental impact from firefighting activities using foam still cause concerns. We have been developing a novel firefighting foam for forest fire with significantly lower environmental risk, consisting of soaps, chelating agent, and diluents. We determined the optimal composition of soap, and found the high biodegradable chelating agent with a high foaming performance.

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